Stabilizing Pd Particles on Nitrogen-Doped Carbon Supports Under Hydrothermal Conditions

Carbon coating has been applied to improve the hydrothermal stability of metal oxide supports for use in aqueous-phase biomass reaction systems. Previously, incorporation of oxygen heteroatoms in the carbon coating were found to provide some enhancement the hydrothermal stability of Pd particles on these carbon-coated materials. To further improve the hydrothermal stability of these Pd particles, nitrogen-doped carbon supports were synthesized. Compared with merely carbon supported Pd catalyst, better dispersion and stability of the particles were achieved with the nitrogen-doped carbon. Unlike with undoped carbon, the Pd particles had limited sintering after extended exposure to hydrothermal reactions conditions and Pd leaching was greatly reduced. Through detailed solid-state ¹³C and ¹⁵N NMR analysis, the carbon surface chemistry was investigated and systematically compared for varying degrees of N incorporation. Previous studies have suggested that heteroatom incorporation could improve stability, but the NMR characterization techniques used in this study allowed for more detailed and quantitative characterization of N species present in the carbon. Better stability was ascribed to nitrogen functional groups including pyridine, pyrrole and secondary amine groups. This work will help to develop a more systematic strategy for improving hydrothermal stability of metal particles by heteroatom doping in carbon supports.